Proving Ground
by LoveNeverDies78
Summary: AU. Regulus is acting as a spy for his brother, passing him information about the Death Eaters. It is a dangerous job, but it's about to get more complicated than either of them could've imagined.


**Greek Mythology Category Competition:** 29\. The Arae - Write about someone using an Unforgivable Curse.

 **The Homework Challenge:** History - Write about the past (Marauders Era)

 **Word Count: 2,143**

 **A/N:** I love writing about a good relationship between Sirius and Regulus. It's been a few months since I've done so, and I've actually had this idea for about a month or so but just got around to writing it.

* * *

"Sirius, what are you doing?" Regulus asks as he storms into his brother's room. "Are you mad? You what'll happen if you leave like this!"

"Be quiet, Reg," Sirius warns him in a whisper. "You have to go along with this."

"What do you mean?"

"I mean you need to take their side," Sirius explains. There is a pounding on the door. The argument Sirius started with their mother downstairs has followed him. "Mother and Father prefer you. They trust you. I need you here." He grips Regulus by the shoulders, holding him at arm's length. "Please. There's a war coming, believe me. I need to know what the family does in all of this."

Realization dawns on Regulus. "You want me to be a spy?"

"I wouldn't ask it of you if I didn't think you could do it," Sirius assures him. "I'm going to fight in this war. Dumbledore's formed an organization to fight and help the Aurors. I'm joining it as soon as I leave Hogwarts. If I have you here, you can help us out, give us information."

"It's dangerous." Regulus is sure Sirius has gone mad. Despite the differences between them and the preferential treatment Regulus receives, the brothers have always had a good relationship. It's been difficult in recent years, but they've made it work. Now Regulus wonders just how much Sirius cares about him. He seems more than willing to put his younger brother in danger.

"I know," Sirius concedes. "I don't like it anymore than you do. I hate having to put you in this position, but it's the only way. I can't make you do it, of course. But I'm asking you, as a favor to me, to please do this."

The pounding intensifies, their mother's shrill voice audible through the wood of the door. Regulus steels himself for what he has to do. Pulling his brother into a tight hug, he says, "Alright."

"Thank you." Sirius hugs him just as tightly. "Remember, no matter what, you must never blow your cover, even if it means saving me."

"Got it." Regulus pushes Sirius away, hard, straight into the door. "You're nothing but a traitor, you know that?" he yells. He smiles at his brother, knowing this is probably the last time they'll see each other for a while.

Sirius returns the smile, and the ruse begins.

* * *

Regulus follows along silently beside his cousin, Bellatrix, as they walk through a forested area. She's been going on and on about having a gift for him. Knowing Bella, it's probably not a normal kind of gift. He's recently been initiated as a Death Eater, although he's so low in rank he might as well have stayed out, but it is helping Sirius stayed informed. Bella promises him that she can get him into the Dark Lord's inner circle, but that it will take time. Regulus will have to prove himself.

"How much further?" he asks, tired of walking.

"Not far at all," she says, "just over that hill."

As they walk, Regulus wonders if Sirius received his letter. They've kept in contact over the years, although at times it has been difficult. While Sirius was still at school, they had to keep up the pretense of hating each other. They couldn't very well speak to each other in the open. So they'd had a designated meeting place. This happened to be the kitchens. They hadn't met very regularly to keep anyone from getting suspicious and the plan seemed to have worked. No one ever caught on, not even their friends.

After Sirius left Hogwarts, they took to writing each other in secret, posting their letters at the nearest owl post office, using fake names. This has remained their safest way of contacting each other as no one has said a thing.

Bella stops him just before they crest the hill. "Now, this gift serves two purposes. First, it's to congratulate you on joining us. Second, it's a way to prove yourself. Pass this test and you'll be in the inner circle in no time at all."

Regulus nods, wondering exactly what she's talking about. A test? No one ever mentioned a test.

They reach a small clearing at the bottom of the hill. A circle of their fellow Death Eaters, numbering about six in all, is shielding something from view. He can see glimpses of whatever it is on the ground between their feet.

"Alright everyone, step aside so my dear cousin can see his gift." Bella giggles, the sound chilling Regulus. She is only happy when she's inflicting pain.

Regulus tries to keep his composure as they step aside. Lying on the ground, unconscious, blood dripping down the side of his head, is Sirius. His hands are bound in front of him. Biting back a gasp, Regulus manages to keep his expression even, his breathing normal. His mouth feels dry, but he forces himself to speak. "What exactly is this?" He attempts to sound as cold as possible.

"Your gift, of course!" Bella exclaims. "This is the easiest way to prove yourself! Kill your worthless brother and the Dark Lord will deem you worthy."

Regulus pales. _Kill Sirius?_ He wonders what Sirius would think of this situation were he awake. Regulus remembers Sirius's words to him on the night he ran away all those years ago: _You must never blow your cover, even if it means saving me._

"What's the matter?" Bella asks, disappointed. "Don't you like it?"

Regulus swallows. "Why is he unconscious? It hardly seems fair that I should kill him like this. What fun is there in it?"

Bella laughs, a cruel, maniacal laugh. "I like your style, cousin!" She takes out her wand and points it at Sirius, who jerks awake, groaning. Bella slowly walks towards Sirius, running a finger along her wand. "Look at you, sleeping when you have a guest. Greet your brother properly." When Sirius doesn't repsond, Bella kicks him hard in the ribs. "LOOK AT HIM!" she screams.

Sirius coughs, a small trickle of blood escaping from the corner of his mouth. He looks up, meets his brother's gaze. Fear flickers across his features, replaced quickly by hatred. Regulus notices this and wonders who Sirius fears for: himself or his brother.

"Now, Regulus," Bella continues, her voice dangerously even once more, "do what you've come to do. Prove to me that you are ready."

Regulus's heart is racing. What can he do? Sirius made it clear that his own safety shouldn't come before Regulus's mission, but he didn't mention this. Unsure what to do, he pulls out his wand and points it at his brother, silently hoping that no one notices how badly his hands are shaking.

"Crucio!" he shouts before he can really think about what he's doing. Sirius writhes in pain, his screams echoing around the clearing. His suffering ends in seconds, his breathing ragged. He coughs up more blood.

"What _are_ you doing?" Bella asks, annoyed. "I said kill him!"

"I want to make him suffer," Regulus answers. "There's no fun in killing him instantly. The Dark Lord likes to make people suffer, doesn't he? Won't this please him?" He is stalling, his mind working quickly to figure a way out of this for both of them.

Bella cackles again. "Oh, this is perfect!" She has, thankfully, bought his excuse. "Oh yes, I do like this! Carry on, by all means!"

 _I'm sorry, Sirius._ He hopes his brother knows this, hopes he knows that this is hurting Regulus as much as it is him. "Crucio!" He feels nauseous as he watches Sirius's agony, but he plasters an evil smile on his face. He has to look like he's enjoying this.

Kneeling down by his brother, Regulus tries to make things more convincing. "Beg me to stop!" he shouts at him. "Plead for death!" Sirius responds by spitting in his face, spattering Regulus with blood.

He is about to cast another Cruciatus Curse when he hears a commotion behind him. They have been ambushed. His fellow Death Eaters are fending off the surprise attack. Regulus, thanking Merlin for their good fortune, drags Sirius into the trees, taking cover behind the remnants of a large stump.

"Sirius, are you alright?" He can't keep the panic from his voice as he unties Sirius's hands. "Please tell me you're alright!"

Sirius tries to speak, but coughs instead. When he composes himself, he says, "Fine, Reg." He grimaces, clutching at his chest. "Hurts to breathe, though."

"I know," Regulus says, his vision blurred by tears. "I'm sorry, Sirius. I'm going to get you out of here. Just hold on, please."

"You aren't going anywhere." Regulus feels the tip of a wand at his neck. "Stand up slowly and you won't get hurt."

Regulus complies, hands held up in surrender. "Please, I-"

"Don't beg me for anything, you worthless scum."

"James, wait," Sirius speaks up. He coughs again, groaning. "It's alright. We can trust him."

"I think you've taken one too many Cruciatus Curses, mate," James replies. "He was hurting you. He's clearly on their side. You've never had one good thing to say about this one, now have you?"

"Thing is-" Sirius grimaces. "I can explain later. Just don't hurt him. Don't do anything. Just bring him back to headquarters."

"Headquarters!" James laughs, disbelieving. "You have gone mad! I'm not bringing him back to headquarters! You might as well go tell You-Know-Who himself where we're hiding."

"Damn it, James, just trust me!" This takes all of Sirius's remaining strength. He falls silent, unconscious once more.

"Great," James grumbles. "I suppose I'm stuck with you now. I'll bring you to Alastor, he'll know what to do."

Regulus allows himself to be lead off, not in the least concerned for his own welfare. His mind is on his brother, injured because of him.

* * *

After a full day of questioning under Veritaserum, Regulus is deemed safe. He is even allowed to join the Order. James seems both surprised and hurt at Sirius's deception over the years.

"He never once told me about you," he tells Regulus once the questioning is over. "You're both good actors. I was completely convinced you despised each other."

"That was how he wanted it," Regulus explains. "This whole plan was his. I just went along with it to make him happy."

* * *

Regulus taps on the open door of Sirius's room. Sirius's face brightens when he looks up and sees his brother. "There you are!" Regulus is relieved to see him awake and much more aware than he was before. This is the first time he's been to visit him since the incident in the forest two days ago. The Healers at St. Mungo's are doing an excellent job of nursing him back to health.

"How are you today?" Regulus takes a seat by the bed, moving his chair to face his brother.

"Better, but tired," Sirius admits. "That took a lot out of me."

"I'm sorry, I was-"

Sirius holds up a hand, stopping Regulus's apology. "No. This isn't your fault. It's mine." Regulus tries to protest, but Sirius stops him again. "I put you in this position. I never thought this would happen. Stupid, really. I put us on opposing sides and think we'll never have to face each other down?"

"I didn't want to hurt you," Regulus says after a short silence. "But I didn't want to kill you, either. I had to do something though, or Bella was going to get suspicious."

"That was clever," Sirius praises him. "You thought quickly and stalled for time. But we were lucky that James and the others showed up when they did. Bella would've made you act before too much longer, I think."

Regulus nods in agreement. "How did she capture you, anyway?" It is something he's been wondering about for the past two days.

"One of our own went missing," Sirius explains. "I was helping with the search. I thought I'd found him, but..." He trails off, not needing to finish. "I don't know how long she tortured me before she brought you along to finish me off. She certainly enjoyed every minute of it." He sighs deeply and closes his eyes.

"I should be going," Regulus says, realizing that Sirius is worn out by even this small amount of conversation. "You need to get some rest."

"Wait." Sirius's hand on his wrist stops him before he can stand to leave. "I'd like you to stay, for a little while at least. It's been so long since we've been able to be together without pretending to hate each other."

Regulus takes Sirius's hand in both of his own and smiles down at him. "Whatever you want, brother. Rest easy, I'm not going anywhere."

Reassured, Sirius quickly drifts off to sleep, Regulus watching over him.


End file.
